The mission of this Program is to prepare a cadre of outstanding cancer epidemiologists through rigorous academic training in research methodology and the epidemiology and biology of cancer, and mentored research. Additional emphasis is placed on molecular and genetic epidemiology methods and applications. A distinguished faculty provides a variety of substantial opportunities for research experience. There are three types of trainees: Doctoral Candidates in Epidemiology includes pre-doctoral candidates either with or without a prior doctoral degree (generally clinicians) who undertake 2-3 years of coursework, in addition to research, in the course of earning a doctoral degree in Epidemiology; Clinical Researchers include physicians with specialty training in cancer preparing for careers in clinical epidemiology who undertake a one year Master's degree program in methodology followed by a year of research; and Post- doctoral Fellows who hold a prior doctoral degree in Epidemiology or in Biology and undertake mentored research (and with coursework if needed) in preparation for an academic career. Those trainee positions are generally awarded for 2 or 3 years. The number of trainee positions requested includes five pre-doctoral students and seven post-doctoral fellows, for a total of 12 trainees. The program had supported 16 trainees since 1998, but at the behest of the NIH project officer, we have reduced the requested number to 12. The Program is based in the Department of Epidemiology of the Harvard School of Public Health, and is also affiliated with the Channing Division of Network Medicine in the Department of Medicine, Brigham and Women's Hospital. A dedicated molecular epidemiology laboratory is available. This proposal continues a long history of excellence in training in cancer epidemiology at Harvard University; the current training program is now in its 37th year, with an outstanding record of achievement in training.